The field of this invention is calipers for detecting internal diameters and more particularly for detecting the variations in internal diameter of pipe or conduit.
Prior art showing calipers of this general kind are shown in U.S. Pat. Nos. 2,638,681, 2,864,173, 2,875,525, 2,907,111, 2,908,085, 2,973,583, 2,990,621, 3,010,212, 2,061,938, 3,075,292, 3,423,671, 3,624,684, 3,641,678, 3,685,158, 3,772,794, 4,109,386, and 4,121,345. These disclosures are intended to serve as background information for the disclosure of the present invention and as such are specifically incorporated herein by reference.
In the calipering of pipe, such as well pipe disposed within a well bore, the caliper tool is placed in the pipe and is moved longitudinally therein to obtain a record of the internal surface variations through the length of pipe. The record obtained shows the condition of the pipe throughout its length. The information generally desired on such a record is whether corrosion or other factors have so reduced or changed the wall thickness of the pipe that it is subject to failure. Information is also of value as to the presence of scale, flattening of pipe, and various other causes for a pipe being other than round.
The caliper tool herein disclosed may be provided with 30, 40, or 60 arms, for example, to provide a detailed record of the casing condition. These tools will detect the remaining casing wall thickness, the minimum inside diameter, perforations, corrosion, buckling, splits, and a variety of other casing anomalies as will be hereinafter described. These tools can be used in oil well tubing and casing I.D.'s as small as about 2" and up to as large as the caliper sizes provided.
Once given by the caliper tool, the casing data is assembled by the uphole equipment into a plotted output as later described.
One object provided by the present caliper tool is that it can be initially and very accurately calibrated at the earth's surface for a subsequent measuring pass of the tool throughout the well casing.
Another object of the present invention is that mechanical wear and slack in the linkage commonly associated with previous calipers is automatically compensated in the linkage.
Still another object accomplished by this invention is accurate translation of longitudinal movement from the feeler arms to a rotary movement which is transmitted to a potentiometer for accurate measurement.
Still another object attained by this invention is the apparatus and method for accurately calibrating the caliper with simulated casing conditions but while the caliper is in an accessable position for calibration at the earth's surface.